Reactor for performing a steam reforming reaction and a process to prepare synthesis gas

ABSTRACT

A reactor vessel for performing a steam reforming reaction having a vessel inlet for natural gas and steam; a vessel inlet for a hot gaseous medium; a vessel outlet for the steam reforming product; and a reactor space which is a bed of steam reforming catalyst, which reactor space inlet is fluidly connected to the inlet for natural gas and steam and at its outlet end fluidly connected with the outlet for the gaseous product; wherein inside the catalyst bed a passageway is provided fluidly connected to the vessel inlet for the hot gaseous medium for passage of hot gaseous mixture counter currently to the flow of reactants in the catalyst bed.

FIELD OF THE INVENTION

The invention is directed to a reactor vessel for performing a steamreforming reaction starting from a natural gas feedstock. The inventionis also directed to a process to prepare a mixture comprising carbonmonoxide and hydrogen from a carbonaceous feed by performing a partialoxidation reaction and an endothermic steam reforming reaction.

BACKGROUND OF THE INVENTION

EP-A-168892 describes an endothermic steam reforming reaction, which iscarried out in a fixed bed situated in at least one pipe in which atemperature of between 800 and 950° C. is maintained by routing at leastpart of the hot product gas from a partial oxidation reaction along thepipe(s). According to this publication the combined partial oxidationand endothermic production of synthesis gas result in a better yield ofsynthesis gas, an increased H₂/CO ratio, a lower usage of oxygen per m³of synthesis gas product obtained and a lower capital cost of the plantfor the production of CO and H₂-containing gas mixtures (as compared topartial oxidation).

A reactor and process for performing a steam reforming reaction isdescribed in DE-A-3345088. This publication describes a reactor vesselfor performing a steam reforming reaction starting from a natural gasfeedstock. The vessel consisted of a tube sheet from which a pluralityof tubes filled with a suitable catalyst extended into the vessel. Therequired heat of reaction is provided by passing the hot effluent of apartial oxidation reaction of natural gas at the exterior of the reactortubes in the vessel. Such steam reformer reactors are also referred toas so-called convective steam reformer reactors.

A disadvantage of the known reactor vessel design is that fouling mayoccur at the exterior surface of the reactor tubes. This fouling willresult in a less favourable heat exchange between hot gas and thecatalyst bed and in time result in a less efficient operation. Short runtimes will result due to frequent shutdowns in order to remove thedeposits. Fouling is especially a problem when the hot effluent of apartial oxidation reaction is used. This effluent is especially suitedfor providing the required heat on the one hand due to its hightemperatures. However the soot present in this effluent will cause theabove fouling problems and for this reason no commercial applicationsdirected to the combined process of steam reforming and partialoxidation such as described in DE-A-3345088 has been developed accordingto our knowledge at time of filing.

EP-A-983964 describes a convective steam reforming reactor vessel,wherein the vessel is provided with a plurality of reactor tubescontaining a catalyst bed. Around the reactor tubes an annular sleeve isprovided to transport a hot effluent of an auto thermal reformer (ATR).By indirect heat exchange between this hot effluent and the reactantspassing through the catalyst bed the steam reforming reaction can takeplace.

WO-A-0137982 discloses a reformer tube of the so-called double-tubeconfiguration of a steam reformer reactor. The double-tube configurationconsists of a reactor tube provided with a catalyst bed in which bed aninner return tube is provided for passage of the reactants beingdischarged from said catalyst bed. The double-tube configuration isdescribed in more detail in U.S. Pat. No. 4,690,690 according toWO-A-0137982. The inner tube as disclosed in WO-A-0137982 has anon-circular cross-section.

WO-A-8801983 discloses a convective steam reforming reactor vesselwherein the hot gas, which is used to heat the reactor tubes, isobtained by burning heating gas in a lower part of the vessel.

The object of the present invention is to provide a reactor design for aconvective steam reformer, which is suitable to make use of a hotgaseous medium, which may cause fouling, as for example the effluent ofa partial oxidation, as the heating medium. A further object is toprovide a process for the preparation of a mixture of hydrogen andcarbon monoxide by a process involving the combination of partialoxidation and steam reforming wherein the problems regarding fouling asdescribed above are minimized.

SUMMARY OF THE INVENTION

This object is achieved with the following reactor. Reactor vessel forperforming a steam reforming reaction comprising:

-   a vessel inlet for natural gas and steam,-   a vessel inlet for a hot gaseous medium,-   a vessel outlet for a gaseous product comprising the steam reforming    product, and-   a reactor space comprising of a bed of steam reforming catalyst,    which reactor space inlet is fluidly connected to the inlet for    natural gas and steam and at its outlet end fluidly connected with    the outlet for the gaseous product, wherein inside the catalyst bed    a passageway is provided fluidly connected to the vessel inlet for    the hot gaseous medium for passage of hot gaseous mixture counter    currently to the flow of reactants in the catalyst bed.

The invention is also directed to a process for the preparation ofhydrogen and carbon monoxide containing gas from a carbonaceousfeedstock by performing the following steps:

-   (a) partial oxidation of a carbonaceous feedstock thereby obtaining    a first gaseous mixture of hydrogen and carbon monoxide and-   (b) catalytic steam reforming a carbonaceous feedstock in a    Convective Steam Reformer comprising a tubular reactor provided with    one or more tubes containing a reforming catalyst, wherein the    required heat for the steam reforming reaction is provided by    convective heat exchange between the steam reformer reactor tubes    and a passageway positioned within and along the axis of the tubular    reactor tubes through which passageway the effluent of step (a)    flows. counter-current to the gasses in the steam reformer tubes.

Step (b) of the above process is preferably performed in the reactorvessel according to the present invention.

DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a possible embodiment of the reactor according to theinvention wherein the catalyst bed is positioned at the shell side of areactor vessel.

FIG. 2 illustrates a steam reformer reactor according to the inventionwherein the catalyst bed is contained in one or more reactor tubes.FIGS. 2 a, 2 b and 2 c illustrate details and preferred embodiments ofthe reactor of FIG. 2.

FIG. 3 illustrates a reactor as in FIG. 2 wherein two separate gasoutlets are provided.

FIG. 4 illustrates the combination of the reactor vessel of FIG. 3 and apartial oxidation reactor vessel.

FIG. 5 illustrates an integrated process involving the installation ofFIG. 4, a Fischer-Tropsch synthesis and some of its downstream unitoperations.

DETAILED DESCRIPTION OF THE INVENTION

Applicants found that by passing the hot gas medium through an elongatedpassageway gas velocity conditions are achieved wherein soot does notadhere or at least adheres significantly less to the heat exchangingsurface of the CSR reactor as compared to the prior art designs.Preferably the elongated passageway is designed such that the gas willflow with a certain velocity wherein the gas has a so-called selfcleaning capacity. The gas velocity at design capacity is preferablyabove 10 m/s and more preferably above 30 m/s. A maximum gas velocity ispreferably below 100 m/s and more preferably below 60 m/s. A furtheradvantage is that if any fouling does occur, such deposits could easilybe removed in a shut down by state of the art methods for cleaning theinterior of conduits. Examples of cleaning methods are pigging andhydrojetting. Further advantages of the above reactor and of itspreferred embodiments will be described below.

FIG. 1 illustrates a reactor vessel (1) for performing a steam reformingreaction according to the present invention. Vessel (1) is provided witha vessel inlet (2) for natural gas and steam, a vessel inlet (3) for ahot gaseous medium and a vessel outlet (4) for the gaseous steamreforming product. Between an upper tube sheet (5) and a lower tubesheet (6) a reactor space (7) comprising of a bed (8) of steam reformingcatalyst is present. Inside the catalyst bed (8) a plurality ofpassageways (9) are provided which start at tube sheet (5) and extend toa tube sheet (10) positioned below lower tube sheet (6). Through thesepassageways (9) the hot gaseous medium flows counter currently to theflow of reactants in the catalyst bed (8). The space below this tubesheet (10) defines a space (11) through which the cooled gaseous mediumis collected and discharged via vessel outlet (12) from the vessel.Between lower tube sheet (6) and tube sheet (10) a space (13) isprovided wherein the natural gas and steam can be distributed and fed tothe catalyst bed (8) via openings (15) in tube sheet (6).

Preferably the passageways (9) are fixed in the lower tube sheets (6)and are allowed to move relative to tube sheet (5) and (10). This willavoid thermal stress at start-up and shut down operations. The openingsmay be filled with a flexible seal, for example ceramic fibre, or can beleft open as for example illustrated in the aforementioned EP-A-983964.The upper end of the passageways (9) is suitably protected by a heatresistant material, for example a ceramic.

FIG. 2 illustrates a preferred reactor vessel (20) for performing asteam reforming reaction according to the present invention. The reactorspace is defined by one or more parallel positioned reactor tubes (21)filled with a bed (22) of steam reforming catalyst. Through thiselongated bed of catalyst one or more passageway(s) (23) for hot gas isprovided parallel to the axis of the reactor tube (21). This passagewayor conduit (23) allows hot gas medium to exchange its heat by indirectheat exchange through the wall (24) of the conduit (23) with the countercurrently flowing gaseous stream present in the catalyst bed (22).

The passageway (23) may have a circular cross-section or a non-circularcross-section such as exemplified in WO-A-0137982. The diameter of acircular passageway (23) is preferably between 10 and 60 mm, morepreferably between 20 and 55 mm. The dimensions of a non-circularpassageway (23) will be such that the same cross-sectional area results.The inner distance between the outer wall of passageway (23) and theinner wall of reactor tube (21) is preferably between 20 and 150 mm.Preferably this distance is at least six times the size of the catalystparticles which occupy this space.

The fact that the catalyst bed (22) is present in an annular spacearound the passageway (23) is advantageous because less thermal stresswill be exercised on the catalyst bed (22) by the tubes (23) at start-upor cool down situations as would be the case in the reactor of FIG. 1.

FIG. 2 further shows a vessel inlet (26) for natural gas and steam, avessel inlet for a hot gaseous medium (27) and a vessel outlet (28) fora mixture of the gaseous product comprising the steam reforming productand the hot gaseous medium. FIG. 2 also illustrates a tube sheet (29)defining a space (30), which fluidly connects the vessel outlet (28)with the outlet of the passageways (23) extending from said tube sheet(29). Also a tube sheet (31) is present below said tube sheet (29)defining a space (32), which fluidly connects the vessel inlet (26) withthe inlet of the reactor tubes (21) filled with catalyst bed (22). Thereactor tubes (21) will extend from this tube sheet (31) downwards. Thepassageways (23) will pass this tube sheet up to the upper tube sheet(29) as shown.

In the reactor as shown in part or all of the product gas of the steamreforming reaction is also passed through the elongated passageways.This is advantageous when the hot gaseous mixture is the effluent of thepartial oxidation reaction preferably having a steam to carbon ratio ofless than 0.5. By combining these streams the steam to carbon ratio ofthe resulting mixture flowing in the passageways (23) will be higher andthereby minimizing metal dusting corrosion within the passageways (23).

Preferably the lower end of the reactor tube (21) is designed such thatimmediate and intimate mixing of the steam reformer product which isdischarged from the catalyst bed (22) and the hot gaseous medium takesplace. FIG. 2 a shows such a preferred embodiment wherein tube (21) andpassageway (23) extend somewhat further than catalyst bed (22). In thisextension openings (29) are present in wall (24) such that a substantialamount of the gaseous effluent from the catalyst bed (22) can enter thepassageway (23) as is indicated with arrow (29′) without being firstemitted into the lower end of vessel (20).

FIG. 2 b shows the upper end of vessel (20) of FIG. 2 in more detail.Also shown are the flow directions of the gasses with the arrows. Aproblem associated with the design shown in FIG. 2 b is catalystremoval. Between tube sheet (29) and tube sheet (31) a small volume ispresent for operators to remove catalysts from the catalyst bed (22).The design shown in FIG. 2 c provides a solution to this problem. FIG. 2c shows the same reactor vessel (20) as in FIG. 2 except that thereactor tube (21) extends together with the passageway (23) to the uppertube sheet (29), while the upper level of the catalyst bed (22) extendsonly to tube sheet (31). In the part of the wall of the reactor tube(21) between tube sheets (31) and (29) an opening (26′) is presentthrough which in use gas can enter as shown. In use the reactor tubewill be fixed in the upper tube sheet (29) by means of cap (26″)(situation a). By removing the top of vessel (20) the individual reactortubes/passageways can be removed from the vessel by removing cap (26″)(situation b) and lifting the reactor tube/passageway combination(situation c). Catalyst can then be easily added, removed or refreshedexternal the reactor vessel (20).

FIG. 3 illustrates a special embodiment of the reactor vessel as shownin FIG. 2. As in FIG. 2 the reactor space is defined by one or moreparallel positioned reactor tubes (21) filled with a bed (22) of steamreforming catalyst, comprising a passageway (23) for hot gas. Adifference with the reactor of FIG. 2 is that a third tube sheet (32) ispresent at the lower end of the reactor vessel (44) defining a space(33) which fluidly connects the vessel inlet (38) for hot gaseous mediumwith the inlet of the passageways (23) which penetrate the tube sheet(32) via openings (34) which are preferably larger than the passageway(23) itself. The fact that the passageways are not fixed in the tubesheet (32) is advantageous because it allows the combined reactor tubes(21) and passageways (23) to freely thermally expand in the reactorvessel (44) at start-up and cool down situations. The lower ends of thepassageway which extends into the lower space (33) may preferably bemade from heat resistant materials like for example ceramics because ofthe high temperatures present in said space due to the fact that herethe hot gaseous medium enters the reactor via vessel inlet (38).

The outlet opening (35) of the reactor tubes (21) comprising thecatalyst bed (22) are positioned just above said tube sheet (32). Thesteam reforming product being discharged from said opening (35) willenter space (36) defined as the space between tube sheets (40) and (32).This space (36) fluidly connects the vessel outlet (39) for the steamreforming product with the openings (35). The space (36) may suitably beprovided with flow directing baffles which will direct the flow of steamreforming product in a zig zag flow through said space therebyoptimising the contact of the hot steam reformer product gas and theexternal surface of the reactor tubes (21) present in said space. In usepart of the steam reforming product being discharged from openings (35)will leave the reactor vessel via outlet (39) and part will leave space(36) via openings (34) to space (33) by operating the reactor such thatthe pressure in space (36) is higher than the pressure in space (33). Inuse preferably from 0 to 60 wt % and more preferably from 0 to 40 wt %of the steam reformer product, as being discharged from openings (35),may enter space (33) to be mixed with the hot gaseous medium. This isadvantageous because the steam to carbon ratio of the gases flowing inthe passageways (23) can be increased thereby limiting metal dustingwithin the passageways (23).

FIG. 3 further shows a vessel inlet (43) for natural gas and steam, avessel inlet for a hot gaseous medium (38), a vessel outlet (39) forsteam reforming product and a vessel outlet (42) for the gasses, whichare emitted from the passageways (23). Tube sheets (40) and (41) arepresent in order to fix the reactor tubes (21) and to define collectingspace (45) for the gasses emitted by the passageways (23) and an inletspace (46) fluidly connecting the vessel inlet (43) for steam andnatural gas and the reactor tubes (21) comprising the catalyst bed (22).

As in FIG. 1 the reactor of FIG. 3 yields two product streams. This isadvantageous when the hot gaseous medium is the product of a partialoxidation reaction, which has a different hydrogen to carbon monoxidemolar ratio than the H₂/CO molar ratio of the steam reformer product.This allows mixing the two streams later on to a specified and desiredH₂/CO ratio. It further allows to obtain hydrogen from the streamcontaining the most hydrogen in a high efficiency. Hydrogen maypreferably be separated from such a stream by for example membraneseparation followed by a pressure swing absorber step. This isadvantageous if the synthesis gas mixture and hydrogen gasses are bothrequired in downstream chemical synthesis processes, for example aFischer-Tropsch process, wherein synthesis gas is required for theFischer-Tropsch synthesis reaction and hydrogen is needed for thevarious hydroisomerisation/hydrocracking and hydrodewaxing units whichconvert the FT synthesis product to for example middle distillates andbase oils.

It will be evident that the reactor as shown in FIGS. 1-3 can also bedesigned up side down and that the variations in tube sheet lay out andcorresponding gas inlet and outlet configurations as illustrated areinterchangeable between FIGS. 2 and 3.

On the interior wall of the passageways (23) as illustrated in FIGS. 1-3and which are in contact with the effluent of the partial oxidationreaction, carbon may form because part of the carbon monoxide reacts tocarbon and carbon dioxide. Aso metal dusting corrosion may occur.Furthermore part of the surface may erode resulting eventually in anunacceptable low mechanical integrity of the passageway tubes. Theseeffects are especially significant when the steam to carbon ratio in thehot gas is below 1, more especially below 0.5. Such gas compositions mayoccur in the above-described embodiments, especially when the partialoxidation of a gaseous hydrocarbon feed is performed in the absence ofadded steam and/or when the feed to the steam reforming step has a lowsteam to carbon ratio.

In order further to minimise the above-described coke formation apreferred material for the passageway is suitably used. The passageway(23), suitably in the form of a tube, is preferably made from a metalalloy, wherein the metal alloy comprises from 0 and up to 20 wt % andpreferably from 0 up to 7 wt % iron. The alloy preferably also containsbetween 0 and 5 wt % aluminium, preferably from 0 up to 5 wt % silicon,preferably from 20 up to 50 wt % chromium and preferably at least 35 wt% nickel. Preferably the nickel content balances the total to 100%.

The tubes and extensions of said tubes are preferably one of thefollowing types: wrought tubes, centrifugal cast tubes or sintered metaltubes.

It has been found beneficial to have at least some aluminium and/orsilicon in the metal alloy surface when the concentration of steam inthe hot gaseous medium within the passageway (23) is lower than 50 vol%, preferably lower than 30 vol % and more preferably lower than 15 vol%. Preferably from 1 up to 5 wt % aluminium and/or from 1 up to 5 wt %silicon is present in said metal alloy under such low steam contentconditions. The resulting aluminium oxide and/or silicon oxide layerswill provide an improved protection against coke formation and erosionwhen the conditions become more reducing at such low steamconcentrations. Examples of suitable metals are Inconel 693 containingaccording to its producer Special Metals Corp (USA), typicallycomprising 60.5 wt % Ni, 29 wt % Cr and 3.1 wt % Al and the Nicrofer6025H/6025HT alloys 602/602CA as obtainable from Krupp VDM GmbH (DE).

The invention is also directed to a process for the preparation ofhydrogen and carbon monoxide containing gas from a carbonaceousfeedstock by performing the following steps:

-   (a) partial oxidation of a carbonaceous feedstock thereby obtaining    a first gaseous mixture of hydrogen and carbon monoxide and-   (b) catalytic steam reforming a carbonaceous feedstock in a    Convective Steam Reformer comprising a tubular reactor provided with    one or more tubes containing a reforming catalyst, wherein the    required heat for the steam reforming reaction is provided by    convective heat exchange between the steam reformer reactor tubes    and a passageway positioned within and parallel to the axis of the    tubular reactor tube through which passageway the effluent of    step (a) flows counter-current to the gasses in the steam reformer    tubes.

An advantage of the above process is that due to the fact that theeffluent of step (a) is passed through well defined passages through thecatalyst bed less fouling on the heat exchanging surfaces of saidpassageways will occur. A further advantage is that the H₂/CO molarratio's of the combined synthesis gas products of step (a) and (b) canbe from 1.5 up to 3 and even preferably from 1.9 up to 2.3 making thesynthesis gas product suitable for various applications as will bediscussed here below.

The carbonaceous feedstock in step (a) is preferably a gaseoushydrocarbon, suitably methane, natural gas, associated gas or a mixtureof C₁₋₄ hydrocarbons. Examples of gaseous hydrocarbons are natural gas,refinery gas, associated gas or (coal bed) methane and the like. Thegaseous hydrocarbons suitably comprises mainly, i.e. more than 90 v/v %,especially more than 94%, C₁₋₄ hydrocarbons, especially comprises atleast 60 v/v percent methane, preferably at least 75 percent, morepreferably 90 percent. Preferably natural gas or associated gas is used.Preferably any sulphur in the feedstock is removed.

Preferably the carbonaceous feed in both steps (a) and (b) is a gaseousfeed as described above. In such a preferred embodiment from 10 to 90 wt%, more preferably from 20 to 50 wt %, of the total gaseous feed tosteps (a) and (b) is fed to step (b).

In step (a) the partial oxidation may be performed according to wellknown principles as for example described for the Shell GasificationProcess in the Oil and Gas Journal, Sept. 6, 1971, pp 85-90.Publications describing examples of partial oxidation processes areEP-A-291111, WO-A-9722547, WO-A-9639354 and WO-A-9603345. In suchprocesses the feed is contacted with an oxygen containing gas underpartial oxidation conditions preferably in the absence of a catalyst.

The oxygen containing gas may be air (containing about 21 percent ofoxygen) and preferably oxygen enriched air, suitably containing up to100 percent of oxygen, preferably containing at least 60 volume percentoxygen, more preferably at least 80 volume percent, more preferably atleast 98 volume percent of oxygen. Oxygen enriched air may be producedvia cryogenic techniques, but is preferably produced by a membrane basedprocess, e.g. the process as described in WO 93/06041.

Contacting the feed with the oxygen containing gas in step (a) ispreferably performed in a burner placed in a reactor vessel. To adjustthe H₂/CO ratio in the gaseous product obtained in the partial oxidationreaction in step (a), carbon dioxide and/or steam may be introduced intothe feed. Preferably up to 15% volume based on the amount of gaseousproduct, preferably up to 8% volume, more preferably up to 4% volume, ofeither carbon dioxide or steam is added to the feed. As a suitable steamsource, water produced in an optional downstream hydrocaxbon synthesismay be used.

The gaseous product of the partial oxidation reaction in step (a)preferably has a temperature of between 1100 and 1500° C. and an H₂/COmolar ratio of from 1.5 up to 2.6, preferably from 1.6 up to 2.2.

Step (b) may be performed by well-known steam reforming processes,wherein steam and the gaseous hydrocarbon feed are contacted with asuitable reforming catalyst in a CSR reactor. The catalyst and processconditions as applied in the steam reformer reactor tubes may be thoseknown by the skilled person in the field of steam reforming. Suitablecatalysts comprise nickel optionally applied on a carrier, fro examplealumina. The space velocity of the gaseous feed is preferably from 700to 1000 litre (S.T.P.)/litre catalyst/hour, wherein S.T.P. meansStandard Temperature of 15° C. and pressure of 1 bar abs. The steam tocarbon (as hydrocarbon and CO) molar ratio is preferably from 0 up to2.5 and more preferably below 1 and most preferably from 0.5 up to 0.9.If such low steam to carbon ratio's are applied in step (b) the catalystpreferably comprises a Group VIII metal. More preferably the catalystcomprises (a) an oxidic support material and (b) a coating comprisingbetween about 0.1 and about 7.0 wt % of at least one of the metals ofthe group consisting of Pt, Ni, Pd and Co, preferably platinum; saidsupport material comprising: (i) at least 80 wt % of ZrO₂ which has beencalcined at a temperature up to about 670° C. before the application ofsaid coating; (ii) 0.5-10 mol % of at least one oxide selected from thegroup consisting of Y, La, Al, Ca, Ce and Si, preferably La₂O₃. Examplesof such catalysts are for example the catalyst described in EP-A-695279.Preferably the feed also comprises an amount of CO₂, wherein preferablythe CO₂ over carbon (as hydrocarbon and CO) molar ratio is from 0.5 upto 2. The product gas of step (b) preferably has a temperature of from600 up to 1000° C. and a H₂/CO molar ratio of from 0.5 up to 2.5.

The temperature of the hydrogen and carbon monoxide containing gas ispreferably reduced in step (b) from a temperature of from 1000 up to1500° C. to a temperature from 300 up to 750° C. The temperature of themetal wall surfaces of the passageway in step (b) is preferablymaintained below 1100° C.

The mixture of carbon monoxide and hydrogen (steam reformer product) asobtained in step (b) may be directly combined with the product gas asobtained in step (a). This may be achieved within the reactor asexemplified in

FIGS. 1 and 3. Alternatively the product gas as obtained in steps (a)and (b) may be obtained as separate streams and optionally combined inany desired ratio.

In a preferred embodiment the steam reforming product as obtained instep (b) is fed to step (a). The invention is also directed to encompassbelow process embodiments wherein a convective steam reactor is usedwhich has separate outlets for the steam reactor product and the cooledeffluent of step (a). An advantage of mixing the steam reformer productof step (b) with the feed to step (a) or more preferably directly intothe reactor of step (a) is that any methane or higher gaseoushydrocarbon, which may still be present in the steam reformer product,is then further converted to hydrogen and carbon monoxide. This isespecially advantageous when the steam reforming step (b) is performedon a feed having a steam to carbon ratio of less than 1, especiallybetween 0.5 and 0.9. Operating the process with a lower steam to carbonratio in the feed to step (b) is advantageous because the resultingsynthesis gas product will then also contain less steam and becausesmaller reactor equipment may be applied. A disadvantage of operatingstep (b) at a low steam to carbon ratio is that more unconverted methanewill be present in the steam reformer product. By routing the steamreformer product to step (a) this disadvantage is overcome.

Optionally the combined streams of step (a) and (b) are subjected to anautothermal reformer step (c) at the elevated temperatures of step (a)in order to convert the gaseous mixture obtained in step (a) to amixture having a H₂/CO molar ratio closer to the desired thermalequilibrium H₂/CO molar ratio values valid for said operatingtemperatures. The combined mixture, optionally after performing step(c), is passed via the passageways to provide the required reaction heatfor performing step (b) to yield the synthesis gas end product.

The above embodiment is illustrated in FIG. 4. FIG. 4 shows the reactorvessel (44) of FIG. 3. For clarity reasons no internals of vessel (44)are shown in FIG. 4. Also shown is a partial oxidation reactor (51)provided with a burner (52). A carbonaceous feed (50) and an oxygencontaining gas (50′) is supplied to burner (52). Also shown is that theproduct gas (55) of step (b) is fed to the upper half of the reactorvessel (51).

Preferably the steam reformer product (55) is fed close, i.e. in theupper half of vessel (51), to the burner (52) in order to benefit themost of the resultant elevated temperatures of from 800 up to 1050° C.present in that region of the vessel (51) enabling conversion of methanewhich may be present in product (55). The methane content in steamreformer product (55) may be between 5 and 30 mol % carbon relative tothe carbon as hydrocarbon in the feed to step (b), (43). This relativelyhigh methane content is a resultant when operating step (b) atrelatively lower temperatures and/or at relatively low steam to carbonratio as described before. Low temperatures in step (b) are suitablybetween 700 and 800° C. as measured on steam reformer product (55) as itleaves the reactor (44). A low temperature is desirable for materialstrength reasons for the internals used in reactor (44).

Another embodiment which aims at operating step (b) such that thetemperature of the reactor (44) internals is kept at acceptable levelsis by allowing on the one hand a higher outlet temperature for steamreformer product (55) and on the other hand reducing the temperature of(56). This is achieved by mixing steam reformer product (55) with thegaseous product of the partial oxidation reaction at a position spacedaway from the burner (52), such that no significant conversion ofmethane present in steam reformer product (55) will take place whenmixing these two streams. Preferably mixing is performed in the lowerpart of reactor vessel (51). Due to mixing of the product of the partialoxidation reaction having a temperature of between 1100 and 1500° C. andsteam reformer product (55) having a considerable lower temperature atemperature reduction relative to the temperature of the product of thepartial oxidation reaction of between 250 and 500° C. will result.

Because the outlet temperature of steam reformer product (55) issuitably higher than in the above described embodiment stream steamreformer product (55) will have a relatively lower methane content,suitably between 1 and 10 mol % carbon and preferably between 2 and 5mol % carbon relative to the carbon as hydrocarbon in the feed to step(b), (43). This methane is preferably converted in a step (c) in whichalso a temperature reduction is achieved of suitably between 20 and 70°C. and preferably between 40 and 60° C. Stream (56) as obtained in step(c) and having a reduced methane content preferably has a temperature ofbetween 950 and 1100° C. and more preferably a temperature between 980and 1050° C. The methane conversion in step (c) is suitably between 10and 50 wt %.

FIG. 4 shows this preferred autothermal reformer step (c), also referredto as catalytic post reforming; when the combined gasses of the partialoxidation reaction and the steam reformer product (55) pass a steamreforming catalyst bed (53) as present in the lower half of reactorvessel (51). The catalyst bed (53) may be any well-known reformercatalyst, for example a Ni-containing catalyst. The effluent of theautothermal reformer step (c) is subsequently fed to inlet (38) ofvessel (44), wherein the gasses are cooled in the passageways (23) (notshown in this Figure) and obtained as the final synthesis gas product(63) via outlet (42).

The synthesis gas (63) as obtained by the above process mayadvantageously be used as feedstock for a Fischer-Tropsch synthesisprocess, methanol synthesis process, a di-methyl ether synthesisprocess, an acetic acid synthesis process, ammonia synthesis process orto other processes which use a synthesis gas mixture as feed such as forexample processes involving carbonylation and hydroformylationreactions. To steps (a) and (b) preferably recycle gases are fed. Theserecycle gasses are obtained in, for example the above exemplified,processes which use the synthesis gas as Prepared by the processaccording to the invention. These recycle gasses may comprise C₁₋₅hydrocarbons, preferably C₁₋₄ hydrocarbons, more preferably C₁₋₃hydrocarbons. These hydrocarbons, or mixtures thereof, are gaseous attemperatures of 5-30° C. (1 bar), especially at 20° C. (1 bar). Further,oxygenated compounds, e.g. methanol, dimethylether, acetic acid may bepresent.

The invention is especially directed to the above process for thepreparation of hydrogen and carbon monoxide containing gas (synthesisgas), wherein additional steps (d) (e) and (f) are also performed. Instep (d) the synthesis gas is catalytically converted using aFischer-Tropsch catalyst into a hydrocarbons comprising stream. In step(e) the hydrocarbons comprising stream of step (d) is separated into ahydrocarbon product and a gaseous recycle stream. Suitably thehydrocarbon product are those having 5 or more carbon atoms, preferablyhaving 4 or more carbon atoms and more preferably having 3 or morecarbon atoms. The gaseous recycle stream may comprise normally gaseoushydrocarbons produced in the synthesis process, nitrogen, unconvertedmethane and other feedstock hydrocarbons, unconverted carbon monoxide,carbon dioxide, hydrogen and water.

In step (e) the recycle stream is fed to step (a) and/or (b). Preferablythe recycle stream is supplied to the burner of step (a) or directlysupplied to the interior of the partial oxidation reactor.

Optionally part or all of the carbon dioxide present in such a recyclestream is separated from said recycle stream before being fed to step(a). Part of the carbon dioxide may suitably be fed to step (a).

Step (d) and (e) may be performed by the well known Fischer-Tropschprocesses which are for example the Sasol process and the Shell MiddleDistillate Process. Examples of suitable catalysts are based on iron andcobalt. Typical reactor configurations include slurry reactors andtubular reactors. These and other processes are for example described inmore detail in EP-A-776959, EP-A-668342, U.S. Pat. No. 4,943,672, U.S.Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720.

FIG. 5 illustrates the configuration of FIG. 4 in combination with aFischer-Tropsch synthesis process unit (64) and its downstreamhydroconversion unit(s) (66). In addition to FIG. 4 FIG. 5 shows how thesynthesis gas (63) is fed to Fischer-Tropsch synthesis process unit(64). In unit (64) a gaseous recycle stream (54) is separated from thehydrocarbon product (65) and recycled to partial oxidation reactor (51).

Also shown is how part (60) of the steam reformer product (55) having arelatively high hydrogen over CO molar ratio is fed to a hydrogenrecovery unit (61) to obtain hydrogen (62) suitably for use inhydroprocessing unit(s) (66).

The molar hydrogen to CO ratio in steam reformer product (55) is higherthan 2, preferably higher that 3 and typically not greater than 6. Thehydrogen recovery unit (61) may be well known membrane separation units,pressure swing absorbers (PSA) or combinations of a membrane unit and aPSA.

In the hydroprocessing units the hydrocarbon product present in (65),comprising typically a relatively large portion of compounds boilingabove 370° C., is converted by well-known hydrocracking andhydroisomerisation processes to middle distillates. Any remainingresidue may be further converted to base oils by catalytic dewaxingprocesses (not shown), which also require hydrogen. Examples of suchdownstream hydroprocessing units are described in for exampleWO-A-0107538, WO-02070631, WO-02070629 and WO-02070627 and in thereferences cited in these publications.

The following examples will illustrate how the reactor according theinvention may be used in a process to make a mixture of carbon monoxideand hydrogen. The values presented are calculated values will come closeto the actual values because use has been made of well knownthermodynamic relations known to the skilled person in the field ofgasification and steam reforming.

EXAMPLE 1

To a steam reformer reactor according to FIG. 2 natural gas and steamare fed in a steam to carbon ratio of 0.75. Also a hot effluent of apartial oxidation reactor is fed via 27 to said reactor. The mass flows,temperatures and resultant product streams are described in Table 1.

EXAMPLE 2

Example 1 is repeated except that the steam to carbon ratio of the feedto the CSR reactor of FIG. 2 was equal to 1.

EXAMPLE 3

In this example the effluent of the reactor tubes was first fed to thepartial oxidation reactor as is illustrated in FIG. 4 (line 55). Nocatalyst bed 53 was present in the reactor 51. EXAMPLE 1 Paralleloperation - steam to carbon ratio of 0.75 Effluent of the partialoxidation Gas leaving the Feed to the Feed to the reac- entering thereactor tubes 21 partial oxidation tor of FIG. 2 via reactor of FIG. 2of the reactor of reactor inlet (26). via (27) flow rate flow rate flowrate flow rate Stream name mol % mol % mol % mol % Component kmol/h(dry) kmol/h (dry) kmol/h (dry) kmol/h (dry) Hexane 0 0.00 0 0.00 0 0.000 0.00 Pentane 0 0.00 0 0.00 0 0.00 0 0.00 Butane 44 0.11 13 0.12 0 0.000 0.00 Propane 186 0.46 56 0.52 0 0.00 0 0.00 Ethane 1,423 3.52 427 3.940 0.00 0 0.00 Methane 21,727 53.75 6,526 60.20 822 1.19 514 1.61Hydrogen 613 1.52 184 1.70 42,624 61.63 20,786 64.91 Carbon 0 0.00 00.00 23,604 34.13 7,171 22.39 Monoxide Carbon 267 0.66 3,368 31.06 1,1491.66 3,285 10.26 Dioxide Nitrogen 886 2.19 266 2.45 886 1.28 266 0.83Argon 76 0.19 0 0.00 76 0.11 0 0.00 Oxygen 15,201 37.60 0 0.00 0 0.00 00.00 Steam 0 0.00 24,543 0.00 5,034 0.00 17,538 0.00 Total 40,424 100.0035,384 100.00 74,195 100.00 49,559 100.00 Molecular 22.99 20.32 12.5314.51 Mass Temperature 353 420 1,273 1,027 (° C.) Pressure 71 73 70 70(bar)

EXAMPLE 2 Parallel operation - steam to carbon ratio 1.0 Effluent of thepartial oxidation Gas leaving the Feed to the Feed to the reac- enteringthe reactor tubes 21 partial oxidation tor of FIG. 2 via reactor of FIG.2 of the reactor of reactor inlet (26). via (27) flow rate flow rateflow rate flow rate Stream name mol % mol % mol % mol % Component kmol/h(dry) kmol/h (dry) kmol/h (dry) kmol/h (dry) Hexane 0 0.00 0 0.00 0 0.000 0.00 Pentane 0 0.00 0 0.00 0 0.00 0 0.00 Butane 45 0.11 12 0.11 0 0.000 0.00 Propane 191 0.46 51 0.45 0 0.00 0 0.00 Ethane 1,456 3.52 387 3.400 0.00 0 0.00 Methane 22,227 53.73 5,908 51.93 822 1.16 200 0.63Hydrogen 627 1.52 167 1.47 43,641 61.65 19,765 62.74 Carbon 0 0.00 00.00 24,167 34.14 6,608 20.98 Monoxide Carbon 274 0.66 4,613 40.54 1,1761.66 4,687 14.88 Dioxide Nitrogen 906 2.19 241 2.12 906 1.28 241 0.76Argon 78 0.19 0 0.00 78 0.11 0 0.00 Oxygen 15,561 37.62 0 0.00 0 0.00 00.00 Steam 0 0.00 32,573 0.00 5,151 0.00 25,816 0.00 Total 41,365 100.0043,951 100.00 75,941 100.00 57,316 100.00 Molecular 22.99 20.62 12.5215.81 Mass Temperature 353 420 1,273 1,027 (° C.) Pressure 71 73 70 70(barg)

EXAMPLE 3 Serial operation - steam to carbon ratio 0.75 Effluent of thepartial Gas leaving the Feed to the oxidation reactor tubes reactor 44of entering the of the Feed to the partial FIG. 4 via reactor 44 ofreactor 44 via oxidation reactor inlet 43 FIG. 4 via 56 55 in FIG. 4flow rate flow rate flow rate flow rate Stream name mol % mol % mol %mol % Component kmol/h (dry) kmol/h (dry) kmol/h (dry) kmol/h (dry)Hexane 0 0.00 0 0.00 0 0.00 0 0.00 Pentane 0 0.00 0 0.00 0 0.00 0 0.00Butane 38 0.10 17 0.13 0 0.00 0 0.00 Propane 161 0.44 73 0.55 0 0.00 00.00 Ethane 1,232 3.34 554 4.23 0 0.00 0 0.00 Methane 18,815 51.06 8,45364.55 313 0.31 1,114 2.86 Hydrogen 531 1.44 239 1.82 63,382 63.39 25,28865.02 Carbon Monoxide 0 0.00 0 0.00 30,775 30.78 9,130 23.47 CarbonDioxide 232 0.63 3,415 26.08 4,323 4.32 3,018 7.76 Nitrogen 767 2.08 3452.63 1,112 1.11 345 0.89 Argon 75 0.20 0 0.00 75 0.08 0 0.00 Oxygen14,998 40.70 0 0.00 0 0.00 0 0.00 Steam 0 0.00 23,727 0.00 21,597 0.0015,393 0.00 Total 36,851 100.00 36,822 100.00 121,577 100.00 54,287100.00 Molecular Mass 23.44 20.21 13.23 13.71 Temperature (° C.) 389 4201,273 1,027 Pressure (barg) 71 73 70 70 C-atoms 22,149 13,262 35,41113,262 H-atoms 85,391 85,819 171,210 85,819 O-atoms 30,460. 30,55861,018 30,558

1. A reactor vessel for performing a steam reforming reactioncomprising: a vessel inlet for natural gas and steam, a vessel inlet fora hot gaseous medium, a vessel outlet for a gaseous product comprisingthe steam reforming product; and a reactor space having a reactor spaceinlet and a reactor space outlet end, the reactor space comprising a bedof steam reforming catalyst, the reactor space inlet being fluidlyconnected to the inlet for natural gas and steam, and at the reactorspace outlet end being fluidly connected with the outlet for the gaseousproduct; wherein inside the catalyst bed a passageway fluidly connectsto the vessel inlet for the hot gaseous medium, the passageway beingsuitable for passage of hot gaseous mixture counter currently to a flowof reactants in the catalyst bed.
 2. The reactor of claim 1, wherein thereactor space is defined by one or more reactor tubes filled with a bedof steam reforming catalyst and wherein said reactor tube comprises oneor more passageway(s) running parallel to the axis of said reactor tube.3. The reactor of claim 2, wherein the passageway is suitable forpassing a mixture of the hot gaseous medium and the steam reformingproduct through said passageway.
 4. The reactor of claim 1, wherein eachpassageway comprises a tube made from a metal alloy, wherein the metalalloy comprises from 0 wt % to 7 wt % iron, between 0 wt % and 5 wt %aluminum, from 0 wt % to 5 wt % silicon, from 20 wt % to 50 wt %chromium and at least 35 wt % nickel, wherein the nickel contentbalances the total to 100%.
 5. A process for the preparation of hydrogenand carbon monoxide containing gas from a carbonaceous feedstock saidprocess comprising: (a) partially oxidizing a carbonaceous feedstockthereby obtaining an effluent comprising a first gaseous mixture ofhydrogen and carbon monoxide, and (b) catalytically steam reforming acarbonaceous feedstock to thereby obtain a steam reformer product, whichcatalytic steam reforming is carried out in a convective steam reformercomprising a tubular reactor provided with a plurality of parallelpositioned steam reformer reactor tubes containing a reforming catalyst,and heat for the steam reforming reaction is provided by convective heatexchange between the steam reformer reactor tubes and one or morepassageways positioned within and along the axis of the tubular reactortubes through which passageway the effluent of step (a) flowscounter-current to the gasses in the steam reformer tubes.
 6. Theprocess of claim 5, wherein the gas velocity in the passageway isbetween 10 m/s and 60 m/s.
 7. The process of claim 5, wherein between 0wt % and 60 wt % of the steam reformer product as obtained in step (b)and the effluent of step (a) flows through the passageway.
 8. Theprocess of claim 5, wherein the hydrogen to carbon monoxide molar ratioof the combined products of step (a) and (b) is between 1.5 and
 3. 9.The process of claim 5, wherein the steam to carbon molar ratio of thefeed to step (b) is between 0.5 and 0.9.
 10. The process of claim 9,wherein the reforming catalyst comprises (a) an oxidic support materialand (b) a coating comprising between 0.1 wt % and 7.0 wt % of at leastone of the metals selected from the group consisting of Pt, Ni, Pd andCo, said support material comprising: (i) at least 80 wt % of ZrO₂ whichhas been calcined at a temperature up to about 670° C. before theapplication of said coating; and, (ii) 0.5-10 mol % of at least oneoxide selected from the group consisting of oxides of Y, La, Al, Ca, Ceand Si.
 11. The process claim 5, wherein the passageways of step (b)comprise metal wall surfaces and the temperature of the metal wallsurfaces is maintained below 1100° C.
 12. The process of claim 5,wherein the steam reforming product of step (b) is fed to step (a). 13.The process of claim 12, wherein the steam reforming product of step (b)is fed to the upper half of a partial oxidation reactor vessel having anupper end, said vessel provided with a burner at its upper end, andwherein the temperature in the upper half of the vessel is between 800°C. to 1050° C.
 14. The process of claim 12, further comprising: (c)autothermally reforming a mixture of the steam reformer product of step(b) and the product of the partial oxidation reaction of step (a). 15.The process of claim 5, wherein hydrogen is recovered from the effluentof step (b).
 16. The process of claim 5, wherein step (b) is performedin a reactor vessel for performing a steam reforming reactioncomprising: a vessel inlet for natural gas and steam, a vessel inlet fora hot gaseous medium, a vessel outlet for a gaseous product comprisingthe steam reforming product; and a reactor space having a reactor spaceinlet and a reactor space outlet end, the reactor space comprising a bedof steam reforming catalyst, the reactor space inlet being fluidlyconnected to the inlet for natural gas and steam, and at the reactorspace outlet end being fluidly connected with the outlet for the gaseousproduct; wherein inside the catalyst bed a passageway fluidly connectsto the vessel inlet for the hot gaseous medium, the passageway beingsuitable for passage of hot gaseous mixture counter currently to a flowof reactants in the catalyst bed.